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Thursday, July 29, 2010

The latest edition of the Carnival of Space, the 164th, is now online over at Next Big Future. This week, space blogs focused on issues such as an updated Lunar Sample Atlas, terrestrial extremophiles, the Mars rover Curiosity, and the distribution of exoplanets discovered by the Kepler telescope.

Wednesday, July 28, 2010

Over the last few days, we have been looking at the geology and volcanic history of Pillan. Pillan experienced a major eruption in 1997 that was seen by the Galileo spacecraft as it was wrapping up its primary mission in Jupiter orbit. In Part one on Monday, we looked at the geology of the region around Pillan Patera and Voyager and Galileo observations of the volcano prior to the 1997 eruption. In Part two yesterday, we focused our attention on Galileo's observations of the eruption itself and how the 10s of cubic kilometers of lava erupted not from the volcanic depression named Pillan Patera, but from a fissure north of the patera. The source fissure was more clearly visible in pre-eruption images, such as those taken in November 1996, as it was largely covered over in images after the eruption. The fissure may be an extension of a fault that bisects Pillan Mons, further indicating that Io's magma often exploit pre-existing faults to reach the surface.

We left off yesterday in March 1998, when Galileo acquired its first detailed view of the eruption site since November 1996. The images showed that lava from the 1997 eruption covered more than 5,600 square kilometers (2,200 square miles) of Io's surface, including the floor of Pillan Patera, where lava poured over the wall of Pillan and down onto the floor of the patera. For a comparison, lava from this eruption covered an area the size of the U.S. state of Connecticut (or the nation of Brunei). Galileo observed the Pillan region using the Near Infrared Spectrometer (NIMS) in May 1998, July 1998, and May 1999. The NIMS observations during this period showed a steady decrease in the power output from the volcano, indicative of cooling lava. By May 1999, the power output seen by NIMS at Pillan was an order of magnitude less than during the peak of the eruption in June 1997 (from Davies et al. 2001). SSI images of Io's trailing hemisphere in July 1999, shown at left, showed slight changes in the Pillan pyroclastic deposit surrounding the eruption site. Most of the western half of the deposit had been subsequently covered over by reddish sulfur from Pele and the northern half was covered up by bright sulfur dioxide frost, likely from sapping from Pillan Mons. Finally, portions of the eastern half of the deposit were covered up by dark pyroclasic and bright plume deposits from the nearby Kami-Nari volcano. These changes further showed that Pillan was much quieter in terms of activity than it was during the eruption in 1997.

On October 11, 1999, Galileo performed its first close flyby of Io since the spacecraft entered orbit around Jupiter in December 1995. The close range of the encounter over Io's trailing hemisphere provided an opportunity for the onboard camera to observe the Pillan lava flow at high resolution (9-18 meters or 30-60 feet per pixel). Unfortunately, due to a camera anomaly, 12 of the 13 images were scrambled, requiring extensive processing to bring out useful information. Despite this processing, most of the images were heavily degraded and included a dark stripe down the center of each frame. The partial full-frame mode image, shown at the lower left of the above mosaic, did not suffer from this anomaly. A rough lava flow emplaced a broad sheet (rather than a channelized flow) was revealed in this mosaic, with pits and lava channels across parts of the flow. Using the length of the shadow along the margin of the flow on the left and right sides of the mosaic, the Pillan lava flow was found to have an average thickness of 8-11 meters (26-36 feet).

The rough texture of the lava surface may have resulted from a number of factors, including the interaction between the hot lava and the cold, volatile-rich surface it flowed over, turbulent flow, and the disconnect between the high effusion rate (the volume of lava flow for each meter of the vent fissure) and the speed of the flow front. In the first case, gas created by the heating of sulfur dioxide frost by encroaching lava flows would burst through the cooled crust of the lava flow. This action would disrupt the cooled lava crust and may form rootless vents that provide gas for the plume seen over Pillan in 1997. One such put can be seen in the left side of the mosaic. Turbulent flow within the lava flow would cause any cooled crust that may have formed to break up into blocks or rafts. These rafts can also disrupt the cooled crust as it is moved downstream by the still molten lava beneath. This can cause gouges to form in the flow field, like the one seen below and to the left of the dark pit on the left side of the mosaic. In the final case, the high lava effusion rate would lead to a crumpling of the lava crust as the flow front advanced at a speed of "only" 0.3 to 1 kilometer per day, the result of the leading edge giving up heat to mobilize surface frost. This would create the rubbly surface texture seen in the October 1999 images.

Galileo observed Pillan from a greater distance on several occasions following the October 1999 flyby of Io. A montage of the SSI observations of Pillan is shown at right. The observations document the gradual fading of Pillan pyroclastic deposits as they are covered by deposits from nearby volcanoes like Pele, Kami-Nari, and Reiden. By December 2000, the deposit was all but invisible except for a faint deposit southeast of Pillan. Interestingly, the multi-spectral color imaging from January 3, 2000 provided the highest resolution color information of Pillan, the source vent of the 1997 eruption, and lava flows. They showed that the flows were greenish in color, perhaps due to the interaction between the still warm lava and sulfur from Pele's plume, producing a layer of impure sulfur mixed with iron (FeS). The observation also showed that the fissure source vent of the 1997 eruption was red in color, similar to other fissures on Io's surface, such as East Girru or the fissure (or lava tube) within the southern end of Lei Kung Fluctus. The Photo-Polarimeter Radiometer (PPR) continued to measure the decreasing power output from Pillan as the Galileo wound down in late 2001 before it plunged into Jupiter in September 2003.

After the end of the Galileo mission, Pillan would be observed from an even greater distance, either from Earth using telescopes such as Keck or the European Southern Observatory or from the New Horizons spacecraft during its encounter in late February 2007. Thermal hotspots were detected at Pillan throughout the 2000s by Keck, suggesting that a low level of volcanic activity continued after the 1997 eruption. Pillan was last detected as a hotspot during a brief observation by Marchis et al. on June 28, 2010. This last observation suggests that Pillan may currently be coming down from a recent eruption.

All was quiet at Pillan during the New Horizons encounter in 2007. The fading of the pyroclastic deposit from 1997 was complete by that point, and the floor of Pillan was once again covered in a thin coat of sulfur frost from the Pele plume, making it show up bright in the LORRI camera images. Only the still dark lava flow north of Pillan Patera suggested that anything had happened at Pillan between 1979 and 2007. No thermal hotspot was observed at Pillan by either LORRI during two eclipses of Io by Jupiter or by the LEISA near-infrared spectrometer.

In 1979, Pillan was a quiet volcano that was not even worthy of a name. But in 1997, a major eruption there allowed scientists to track the changes it created on Io's surface at a close range. The eruption became the archetype for fissure-fed eruptions on Io, producing large-scale surface changes, areas of incandescent lava, and lava fountains at the source vent. Similar, even more powerful eruptions would later be seen at Surt and Tvashtar. Potentially, the East Girru eruption seen by New Horizons may be most similar to what happened at Pillan in 1997, though the short duration of the encounter prevented follow-up observations of East Girru.

Thanks for reading this week's premiere of my "Io Volcano of the Week" series! If you haven't already, I encourage you to read Parts One and Two of my profile of Pillan. Next week I will be profiling a volcano that should only require one post to discuss: Zal Patera.

Yesterday, we took a look at the volcano Pillan Patera and its surroundings prior to its eruption in 1997. In our look back, I took you all the way to April 1997, on the eve of the eruption. To that point, Pillan had been a fairly nondescript, 75-kilometer (47-mile) wide patera that only been seen as a weak thermal hotspot on a pair of occasions in November 1996 and February 1997. This would change beginning in May 1997, when the Near-Infrared Spectrometer (NIMS) onboard the Galileo spacecraft detected a much brighter hotspot at Pillan, suggesting that a major eruption had begun. Later modeling by Davies et al. suggested the presence of lava with a temperature of at least 1500 K covering an area of 0.2 square kilometers (50 acres). Such high temperatures are consistent with large lava fountains or turbulent lava flows, where massive amounts of extremely fresh lava could be detected. Despite the detection of a bright eruption at Pillan by NIMS during Galileo's G8 orbit, Pillan looked no different in distant images taken by the SSI camera than it had in earlier orbits. This suggests that the Galileo observations on May 7, 1997 captured the eruption at a very early stage, before any large lava flows had formed. This is validated by the low-temperature component in the Davies et al. paper on the eruption styles of Pele and Pillan, which found the area of fresh lava flows 5-10 minutes old covered an area of 31 square kilometers (12 square miles). This provides another link to the East Girru eruption seen by New Horizons 10 years later. New Horizons also appeared to have caught that eruption in its early stages, before it had a chance to produce any major surface changes. Perhaps if we were to revisit Io today, a fading pyroclastic deposit and lava flows field would be seen around the East Girru fissure.

Galileo returned to the inner Jupiter system in late June 1997 during orbit C9, allowing Io to be observed in daylight and in eclipse on June 28, 1997. In the case of the daylight image, shown above, a new plume ~110 kilometers tall was observed over Pillan on the limb of Io. Before that observation, no plume had ever been observed at Pillan. In fact, when Hubble imaged the Pillan plume on July 22, 1997, it was initially thought that the plume came from the nearby Reiden Patera. Unlike the plumes from other outburst eruptions such as at Grian Patera in 1999 or Tvashtar Patera in 2007, rather than being a large, gas-rich plume, Pillan's plume was much more dust-rich, approaching Prometheus's prominent plume in brightness and mass (see Geissler and McMillan 2008). By analogy with similar plumes on Io, this suggests that the Pillan plume resulted from the interaction between hot silicate lava and cold sulfur dioxide frost on the surface of the plains the lava flowed over, rather than direct outgassing from a volcanic vent. Pillan was also seen in eclipse images taken 16 hours later. Again, evidence that an intense eruption was taken place at Pillan was observed. An intense hotspot was seen over the volcano in both SSI and NIMS data (though the low resolution of the later meant that the NIMS pixel covering Pillan also covered the active Pele volcano).

Initial modeling from the SSI and NIMS C9 observations provided tight constraints on the eruption temperature of Pillan's lavas, suggesting temperatures that were above the range of terrestrial basalts, but were instead in the temperature range of ultramafic lava, last seen on Earth two billion years ago. These temperatures, 1800-1900 K (lower limits actually), also caused problems for modelers when it came to the amount of melt required in the Ionian asthenosphere. Tidal heating models required a mantle with a much smaller melt fraction than would be required by the super high eruption temperatures estimated for Pillan. However, more recent modeling by Keszthelyi et al. 2007, that better accounts for lava fountaining, now place a lower limit on the eruption temperature at Pillan closer to 1610 K, within the range of terrestrial basalts.

The first visible images of the effects of the eruption came on September 19, 1997, when Galileo returned to the inner Jupiter system for the 10th time. This multi-spectral set (10ISIOGLOC03) revealed a dark spot more than 400 kilometers (250 miles) across and a fresh lava flow with an area of 3,100 square kilometers (1,200 square miles). This data allowed researchers to better understand the geologic context for the eruption. Rather than being located with Pillan Patera, the eruption started from a fissure located to the north of the volcano. Fresh lava flows extended south and east from the southern end of this fissure. The dark spot that surrounded the Pillan lava flows were likely the result of pyroclasic flows that hugged the ground and deposited a thin layer of dark basaltic tephra. This hypothesis is supported by the visible and near-infrared spectra of this deposited, as derived from this image set. Geissler et al. 1999 found evidence for iron-rich orthopyroxene (enstatite end-member), a mafic mineral, within the dark deposit. NIMS and SSI observations of Ionian hotspots in September 1997 also revealed that the eruption was still on-going, with significant areas of incandescent lava still visible.

Galileo took a few more peaks of Pillan in late 1997 and early 1998, as the spacecraft began its first extended mission. In November 1997, SSI observed Pillan's plume, fainter and slightly taller than it was June of that year, as well as the thermal emission from the volcano during an eclipse observation. This time, two hotspots were seen: one corresponding to the source fissure and a brighter one to the south corresponding with the southern portion of the flow field and Pillan Patera. This suggested that lava from the Pillan eruption was flowing over the edge of the patera and down onto the floor of Pillan Patera, like a two-kilometer tall lava fall. Sure enough, this was confirmed four months later, when Galileo SSI observed Pillan at only 2.6 kilometers (1.6 miles) per pixel. The floor of Pillan Patera had darkened, likely from lava from the eruption flowing down from the north and covering the 2,500-square-kilometer (950-square-miles) patera floor. Thus, by March 1998, the Pillan eruption of 1997-1998 had resulted in 5,600 square kilometers (2,200 square miles) of new Ionian terrain. Assuming an average thickness of the lava flow was 10 meters (a reasonable number given later observations), then more than 56 cubic kilometers (13 cubic miles) flowing from the source vent during the eruption. For comparison, the Laki eruption in Iceland in 1783, one of the largest eruptions ever observed on Earth, produced more than 14 cubic kilometers (3.4 cubic miles) of lava.

Believe it or not, there is just too much to talk about with respect to Pillan to cover in just TWO blog posts. More specifically, I am tired and hungry, so I am going to cut this installment short. But have no fear, I will be back tomorrow with a discussion of the high resolution observations of the Pillan flow field from Galileo and more recent observations of the volcano.

Monday, July 26, 2010

Beginning this week, we will take a look at one of Io's hundreds of volcanoes each week. For this premiere post, we will take a look at Pillan, a volcano that is notable for its large eruption during the Galileo Nominal Mission in 1997. The eruption resulted in a dark, pyroclastic more than 400 kilometers (250 miles) across, a fresh lava flow with an area of 3100 square kilometers (1,200 square miles), and a deposit created by a dusty plume 100-120 kilometers (60-75 miles) in height that partially covered the iconic red ring plume deposit of Pele. The massive eruption, one of the most significant observed by Galileo in terms of energy output and the areal surface coverage of the fresh lava, began in May 1997 and was in full swing by June 28 when the SSI camera onboard Galileo detected a bright hotspot at the volcano when the instrument observed Io while the satellite was in the shadow of Jupiter. And to think, nothing strange had ever been noted at this volcano.

Voyager and Galileo images of Pillan before its eruption

Pillan Patera was first seen during the Voyager 1 encounter in March 1979, the first time Io's surface had been seen in any kind of detail. Voyager scientists were astonished by the sheer number of volcanic features on Io's surface. However, Pillan was not of much interest. The volcanic depression was not even named until shortly before the eruption in 1997. It was seen at a resolution of 500 meters (1,640 feet) per pixel in the large south polar mosaic, so the lack of interest wasn't for lack of good images of the region. Image number 1 at right shows the region around Pillan. You can see Pele, a persistently active lava lake near lower left. Pillan wasn't really distinguishable from the surrounding terrain, if it weren't for the two kilometer high margin that separates the floor of the patera from the surrounding plains. The image does provide some details about the nearby terrain that was not seen at this kind of detail by Galileo. To the north of the speech-bubble shaped patera is a mountain now named Pillan Mons. This mountain is bisected by a pair of fractures and appears to be in a state of collapse with a landslide deposit on the northeast side of the mountain. This deposit is frequently coated in bright sulfur dioxide frost, perhaps from sapping from the mountain. Between Pillan Patera and Pillan Mons is the V-shaped source fissure of the 1997 eruption. During the Voyager mission, this fissure was surrounded by bright material, likely older lava flows that have been coated in sulfur and sulfur dioxide after an earlier eruption. Interestingly, some of these flows have the same shaped as the 1997 flows. Once again on Io, eruptions have happened the exact same way before, and they will do so again.

Galileo entered orbit around Jupiter in 1995 and imaged Io on a semi-monthly basis starting in June 1996. Many of these early images, intended to monitor changes in the plume deposit around Pele, also revealed apparently changes at Pillan Patera. Were these real changes? During Galileo's first orbit in June 1996, Pillan Patera appeared brighter than its surroundings (see image 2 above). However, it had darkened considerably by September 1996 during the next orbit. Was this due to an eruption? Galileo would observed Pillan at even higher resolution during C3, the next orbit in November. This time, Pillan had the same albedo as its surroundings. Was this due to rapid surface changes? Turns out, it was due to an odd phase function of the surface materials on the floor of the patera. When Pillan was viewed at low phase angles, like G2 and later in E6 in February 1997, the surface appears dark. When viewed at higher phase angles, the surface appears brighter. This is the result of a thin layer of bright sulfur dioxide frost coating dark silicate materials on the patera floor. This makes the floor of Pillan quite forward scattering. You can see a similar effect taken to extremes near Loki in New Horizons images. In terms of volcanic activity, some slight activity was seen by the Near-Infrared Mapping Spectrometer (NIMS) in November 1996 and February 1997, but neither detections approached the level of activity seen later in the nominal mission.

Two Fissures: Pillan from Nov 1997; East Girru from Oct 1999

Special attention should be paid to the clear filter images from November 1996, the highest resolution data set of the Pillan region from Galileo prior to the eruption. The image clearly shows the carrot-shaped ^ of the 1997 eruption source. It appears as a thin, dark fissure in this image, which would be around six kilometers wide based on this data. Surrounding this thin fissure is a diffuse region of darkish material. A similar albedo pattern is seen at other Ionian fissures, such as within Lei Kung Fluctus, and most intriguingly at East Girru, shown paired with the November 1996 image of Pillan. East Girru was the source of a bright eruption that was just getting going during the New Horizons flyby in late February 2007.

Unfortunately, I am going to have to cut this installment short (I want to get to Best Buy for the midnight sale of Starcraft II). Have no fear, tomorrow, when I am not working (or playing Starcraft II), I will continue this tale of fire fountains and black eyes tomorrow evening. We will explore the significance of the shape of the Pillan eruption source vent. We will also look at Pillan's impact on our knowledge of Io and its interior. Finally, we will look at how the model it inspired was undone.

Thursday, July 22, 2010

JPL will be host a webcast and chat on their Ustream channel at http://www.ustream.tv/nasajpl covering outer planet satellites like Io. The topic is called "Moons: The Weirdest Planets in Our Solar System" and has the following description:

Moons are fantastic worlds - with features unlike anything seen on Earth: giant sulfur-spewing volcanoes, globally cracked ice-covered surfaces, liquid lakes of hydrocarbons, and colossal watery plumes. Many of these worlds also happen to be the most likely places for life to evolve outside the Earth. How cool is that?

Wednesday, July 21, 2010

The popular BBC Two series, "Wonders of the Solar System", is finally making its way to this side of the Atlantic. The first episode, "Empire of the Sun" premieres on the Science Channel on Wednesday, August 4 at 9pm EDT/6pm PDT. The show, hosted by Brian Cox, was well received when it aired in the UK earlier this year. It covers various aspects of planetary science, from the Sun in the first episode, the formation of the Solar System and Saturn's rings in the second, planetary atmospheres in the third, geology in the fourth, and the role of water for life on Earth and elsewhere in the fifth. A significant section on Io, its volcanic activity, and the terrestrial lava lake analog at Erta'Ale will air in the fourth episode, "Dead or Alive."

Thankfully, while it looks like they have changed the music, the world-wide version will have the same host as the BBC one, though given that he is an on air host, I don't really see how else you can do it. But at least they are not replacing him with Oprah.

In addition to airing next month, the series will also be released on Blu-ray and DVD on September 7. Strangely enough, the Blu-ray version is cheaper on Amazon.com than the DVD. Good news for me ;-)

Well, I should finally get to writing up an article on a new paper out this month in the Journal of Volcanology and Geothermal Research on Io titled, "The thermal signature of volcanic eruptions on Io and Earth." The authors for this paper are Ashley Davies (pictured at right with the nice manly man-beard), Laszlo Kestay (formerly Keszthelyi), and Andrew Harris. Unfortunately, my delay in writing something up about this paper for the blog has meant that other bloggers have had time to scoop me. Seriously, how was I to know that someone would write up a post about an Io paper before me? This hasn't really happened before. You can read Emily Lakdawalla's excellent discussion of Ionian volcanism and this paper's treatment of it on her Planetary Society Blog. Davies emailed out copies of the paper to various Ionians and Emily, which as Emily states, is something other scientists should take note of. However, I have to one up Emily just a little bit. He told me about the paper personally last week :-p So there! Though maybe my parody ads for Io have had some effect after all?

Anyways, enough with my professional jealousies [humor using hyperbole alert!], let's get to the paper, shall we. In the article, the authors investigate methods for identifying volcanic eruption styles using low spatial resolution, near-infrared data. This is particularly useful for Io, as the only thermal observations available of Io have a resolution of at best a few kilometers per pixel but more typically have pixel sizes of tens to a couple hundred kilometers across. The problem of spatial resolution is compounded in more recent data from the Keck telescope, where observations are typically acquired at only a few wavelengths between one and five microns. Just last week, Franck Marchis showed off data on his blog showing Io at three such bandpasses from the Keck telescope at 2.1, 3.8, and 4.7 μm. Davies and his two co-authors also examined satellite data of terrestrial volcanoes, which could then be compared with observational ground-truth. This provided a way to test their method.

Davies and his co-authors determined that by examining the ratio between thermal output at two and five microns of a volcano in Galileo NIMS or ground-based data and tracking how that ratio changes with time, they could characterize the style of volcanic activity. These different styles include open-channel or insulated lava flows (like those seen at Kilauea), lava fountains, lava lakes, lava domes, silicic lava flows, though the latter two, while important volcanic features on Earth, have not been identified on Io. This works because the peak wavelength for the thermal emission of a lava flow or lava lake shifts to longer and longer wavelengths as it cools. Basaltic lava that has only been cooling for one second has a peak thermal emission wavelength of two microns, while the thermal emission of lava that has been cooling for more than seven hours (or two hours on Earth) peaks around five microns.

So more vigorously active eruptions will have more fresh lava exposed than older, more quiescent eruptions, and thus will have greater 2 μm : 5 μm ratio. More active volcanic eruptions include Tvashtar's back in 1999 and 2007, when lava curtains were observed at one of its constituent paterae. The eruptions of Pillan in 1997 and Surt in 2001 also fit this model, with Surt having a 2 μm : 5 μm ratio of 2. Also typical of these outburst eruptions is their short duration. Over time, the 2 μm : 5 μm ratio at these eruptions decreases as the fire fountaining ceases and the thermal emission becomes dominated by large areas of cooling lava. The volcano I profiled on Sunday maybe in this stage. High 2 μm : 5 μm ratios can also be found at vigorous lava lakes such as Pele, where smaller lava fountains balance out the emission from the cooled lava crust that covers most of the lake. Similar activity such as this can be seen at a much smaller scale at the Erta'Ale lava lake in Ethiopia, shown at night in the image at the top of this post and at above right.

Quiescent eruptions, such as those with insulated lava flows (where lava flows from the source to the flow front via lava tubes) or episodically overturning lava lakes, have much lower 2 μm : 5 μm ratios as their thermal emission is dominated by cooling lava with only small areas of recently emplaced lava. Such activity can be seen at Io's large, persistent flow fields like Amirani, Zamama, and Prometheus or the multitude of volcano depressions like Altjirra Patera.

Combined with analysis of terrestrial data, the authors found that low 2 μm : 5 μm ratios typified volcanic eruptions with "older surfaces, increasing insulation [more lava flowing through lava tubes to breakouts], and quiescent emplacement". Eruptions with a high 2 μm : 5 μm ratio (> 0.5) suggest the presence of "younger [flow] surfaces, decreasing insulation, and more violent emplacement. Eruptions with greater overall radiant fluxes have increasing effusion rates and lava with lower viscosity and less silicon dioxide (less silicic). This ratio must also be combined with repeat observations for temporal coverage. This allows for the disambiguation between vigorously active lava lakes, open-channel lava flows, and lava fountains, for example, which are active for different timescales.

Finally, the authors provide suggests for applying their method to data from future spacecraft to the Jupiter system and Io. For example, they suggest that temporal resolution trumps spatial and spectral resolution for monitoring the progress of a volcanic eruption, particularly for understanding processes at different temperature regimes (though high spatial resolution observations are great for spotting small scale features like skylights over active lava tubes). For example, observations with a temporal resolution on the order of 1-10 seconds, or less, are useful for obtaining temperatures from vigorously active lava bodies such as lava fountains. Observations with scales on the order of a few minutes to hours are useful for monitoring changes in the flow rate at open-channel lava flows, while lava lakes and insulated lava flows can be observed on a daily to weekly basis. They also suggest that thermal imagers on future spacecraft use a few, select wavelength windows such as 2 and 5 microns, and others in the thermal infrared between 8 and 12 microns for monitoring different volcanic eruption styles.

Sunday, July 18, 2010

On Friday, I posted a note about Franck Marchis' observations of Io using the Keck Telescope's adaptive optics system on June 28, 2010. These observations allow us to sneak a peek at the ongoing volcanic activity on Io's anti-Jovian hemisphere. Their images revealed hot lava at several volcanoes like Pillan Patera (the most intense hotspot seen on that date), Isum Patera, Marduk, Prometheus, and Volund (not Zamama as previously suspected). These hotspots were seen in both 3.8 μm and 4.7 μm wavelength images, in the near infrared. Hotspots were seen in only the 4.7 μm wavelength image, indicative of more cooled lava, at Rata Patera, Culann Patera, near Kurdalagon Patera, Tupan Patera, near a patera at 42.5 South Latitude, 172.5 West Longitude, and at a patera located at 6 degrees South, 190 degrees West. All but the last of these hotspots was seen before by either Galileo or New Horizons as active volcanoes. None of these hotspots were seen in the 2.1 μm image, suggesting that none of these volcanoes were vigorously active on June 28. The 2.1 μm instead showed Io's surface in reflected sunlight. Silicate materials show up as dark in the 2.1 μm image, while sulfurous materials show up as bright.

Now as Franck pointed out, this isn't the most exciting set of results. Save one new hotspot, all the others were seen as active before and none are currently in an outburst phase. But regardless, it is important to observe Io more often to understand what is typical in terms of volcanic activity on the satellite. How often do outbursts occur? You are not going to know that if some observing days reveal none. Exciting, okay, maybe not, but VERY useful.

Anyways, I was a bit curious about the one exception to this "boring" fest, the new hotspot at 6 degrees South, 190 degrees West. The patera this hotspot seems to be associated with is 60 kilometers by 45 kilometers in size. The image at left shows various views taken by Galileo during its mission between November 1996 and October 1999. As you can see, no changes were observed at this volcano during the Galileo mission, nor did the volcano look any different in New Horizons images taken in February 2007. While the 2.1 μm image from Keck has a very low resolution (150 km or so), there does seem to be dark spot associated with this volcano that would indicate the emplacement of dark lava, whereas before, the floor of the patera was covered with sulfurous materials.

Very intriguing stuff that at least one volcano on Io seems to have reawakened.

Friday, July 16, 2010

Believe it or not, but public information on recent volcanic activity on Io has been pretty limited. In fact the last report on Io's volcanic activity that is available to discuss here came during the New Horizons encounter back in late February 2007, more than three years ago. Thankfully, that information drought has finally, mercifully come to an end! Franck Marchis posted on his blog at Cosmic Diary results and images he and one of his undergraduate assistants, Keaton Burns, of Io on June 28.

Using the adaptive optics system on the W.M. Keck II telescope on the Big Island of Hawai'i, Marchis was able to image Io at several near-infrared wavelengths during a break between searching various asteroids for satellites (a project Marchis has previously been quite successful with). On his blog, Marchis posted a set of images taken at 2.1 μm (Kp), 3.8 μm (Lp) and 4.7 μm (Ms) of Io's anti-Jovian hemisphere. The 2.1 μm image shows mostly reflected sunlight, but the other two reveal thermal emission from Io's volcanoes. More volcanoes are visible in the 4.7 μm image because cooler (read older) lava can be detected at longer wavelengths. Both the 3.8 μm and the 4.7 μm images revealed emission at the usual suspects like Marduk, Prometheus, and Zamama, with the most intense hotspot located at Pillan. Looking at the image myself, you can also see additional, fainter hotspots can be seen at Rata, Culann, and Isum, as well as a new hotspot near a volcano at 6 degrees South, 190 degrees West.

I need to head out the door right now, so I will definitely have more when I get back.

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I work for the Cassini Imaging team, usually processing Titan and Enceladus images and making maps of Titan based on our images. When I am not working or studying, I'm...I forget. I watch a lot of movies I guess.